IMD's are used today in a variety of applications. In general IMD's include a connector assembly that has one or more electrical receptacles each adapted to receive a corresponding lead and to connect the lead to electronic circuits within the IMD. By way of example, an IMD may be a cardiac pacemaker, or other implantable stimulation device, such as a cardioverter or a defibrillator. By way of further example, an IMD may also be an appetite suppression device, a nervous or muscle stimulation device, a pain reduction device, a medicine delivery device, and the like. The IMD includes a hermetically sealed housing or casing (sometimes also referred to as a “can”) to isolate the electronic circuits contained within the device from the body environment. Such devices require that electrical signals be reliably passed between the sealed circuitry and external connectors without compromising the isolation of the electronics. Depending on the configuration of the IMD there may be multiple electrical paths that extend between the device and the external connectors to deliver, for example, multi-chamber or multi-site stimulation and shock therapy, and to receive sensed cardiac signals. The electrical paths must be electrically and mechanically integrated with the device to provide a safe, long-term connector assembly that does not compromise the hermetic package.
Typically, the housing is provided with a feedthrough assembly that electrically couples the electronic circuits contained within the device housing to the connector assembly. The feedthrough assembly extends through the wall of the sealed casing to the connector assembly and couples the electronic circuits within the casing to lead-receiving receptacles within the connector assembly. Each lead has one or more electrical terminals on a proximal end thereof, typically in the form of a pin terminal and one or more conductive ring terminals. The pin may be electrically coupled to a distal tip electrode. When the proximal end of the lead is inserted into the lead receptacle of a connector assembly, contacts within the receptacle engage corresponding pin terminals on the lead to couple the lead to the electronic circuits within the IMD via the feedthrough assembly. A dependable electrical connection is made and retained between the lead terminals and the corresponding connector assembly contacts. At the same time, the connector assembly must be capable of releasing the lead from the lead receptacle during explanation or other subsequent procedures, and must also tightly seal against entry of body fluids.
Conventional connector assemblies electrically and mechanically connect the proximal end of the lead within a receptacle of the connector assembly by means of a variety of captive fastening screw/collet arrangements and setscrews. In prior art connector assemblies in which the lead is fixed within the lead receptacle using a setscrew, the setscrew is often threaded into an electrical connector block within the connector assembly. When the screw is advanced, it comes into contact with an associated terminal on the proximal end of the lead, mechanically and electrically coupling the lead and the connector assembly. However, the proximal end of a lead is sometimes damaged by an over-tightened setscrew. Also, the setscrews may strip out of the threaded connector block. To address such problems, large setscrews of a certain physical size have been employed. The result is that the setscrew protrudes from the side of the connector assembly, which becomes more noticeable as the physical size of the IMD and connector assembly is reduced.
A further problem of prior art setscrew type connector assemblies arises from the need to isolate the setscrew and the setscrew block from body fluids. One solution has been to use a silicone seal called a septum. The septum forms an insulation barrier between the setscrew and body fluids. However, the septum must permit a wrench to pass through the septum so that the setscrew can be tightened. Frequently, the septum is damaged by the wrench resulting in a loss of the isolation barrier.
Accordingly, it would be desirable to provide a retaining mechanism for a connector assembly for securing and locking the proximal end of a lead to an IMD which will prevent complete retraction or removal of the retaining mechanism from the connector assembly.